Sometimes it's the mundane things you notice most, and one small detail stuck in the mind particularly yesterday after viewing Britain's first two zero-carbon homes: no radiators.
Other more exotic features, from rooftop wind turbines and solar panels to grey-water recycling systems, were more glaringly obvious at the two state-of-the art houses built to generate virtually no greenhouse gas emissions in their running, and unveiled at an exhibition of new construction methods.
But in the end it was the absence of radiators that seemed to symbolise what was truly different about these homes of the near future. The Government has decreed that their like will have to be the model for all new homes from 2016.
In each case the biggest problem, in terms of countering the contribution to global warming of our housing stock - how to provide heat energy - had simply been designed out.
Completely airtight and swaddled in thick insulation - though you can't see it - both the Lighthouse, built by the building materials company Kingspan Off-site, and the Sigma, constructed by the Stewart Milne Group, need much lower levels of power than conventional homes, for space heating, water heating, lighting and running appliances, from computers to refrigerators. And in theory, virtually all of this can be provided by the renewable energy that each house generates itself.
Both went on show yesterday as part of a group of five demonstration buildings, built to the Government's new code for sustainable homes, at the innovation park of the BFE (Building Research Establishment) in Watford.
They are thought to be the most advanced homes of their type in the world. The code, a voluntary regulation introduced in April, is a measure of environmental sustainability for new houses, focusing on substantial reductions in CO2 emissions and water use. It starts to become mandatory at higher and higher levels after next year, and by 2013 new homes will have to achieve level 4 - which means 44 per cent more carbon efficient than current building regulations specify.
Three of the homes on show achieve level 4, but the Sigma achieves level 5, which means zero carbon for space and water heating and lighting, and the Lighthouse the top level, 6, which means zero carbon for everything including use of electrical and electronic appliances. Level 6 will be the national standard from 2016.
Both are timber-framedhouses of modular construction and the parts are factory-built and assembled on site, which means that walls have a much tighter fit, enabling the houses to be airtight to prevent heat loss. The much smaller amount of heating necessary is supplied in the Sigma by a gas boiler, supplemented by solar water heating, and in the Lighthouse by a biomass-burning combined heat and power boiler.
The Sigma has three wind turbines on the roof, and some photovoltaic cells to generate electricity; the Lighthouse has an extensive photovoltaic array. The Stewart Milne Group said the cost of the renewable energy equipment would add about £40,000. But both companies, which plan to produce the houses for sale, said these costs were continually falling.
Yvette Cooper, the Housing minister, took a tour of both houses yesterday. "A quarter of carbon emissions come from our homes," she said. "That is why zero carbon homes are so important. We need a complete revolution in the way we design and build our homes."Reuse content